JP7461479B2 - Chemical conversion treatment composition for Zn-Al-Mg alloy plated steel sheet and Zn-Al-Mg alloy plated steel sheet - Google Patents

Description

The present invention relates to a composition for chemical conversion treatment of a Zn-Al-Mg alloy plated steel plate and a Zn-Al-Mg alloy plated steel plate.

In general, zinc and zinc-based alloy plating is used to prevent or reduce metal corrosion. However, as the amount of zinc used in nature increases, the price of zinc metal is rising and zinc depletion is becoming a problem. As a countermeasure, methods are being taken to reduce the amount of plating by using plating with excellent corrosion resistance that includes the addition of alloying elements. As part of this, many alloy platings that add aluminum and magnesium to zinc have been developed and have been used mainly for construction, but recently there has been a trend for their use to be expanded to home appliances and automobiles as well. In particular, chromate coating, which has excellent corrosion resistance, is often used to protect the surface of Zn-Al-Mg alloy-plated steel sheets, improve corrosion resistance, and make parts easier to process.

However, the biggest problem with these alloy-plated steel sheets and chromate-treated steel sheets is the blackening phenomenon that occurs on the surface of the plating layer during long-term storage at the client's facility, condensation due to temperature differences, or storage in a coiled or stacked state in a hot and humid environment. This blackening phenomenon is a common phenomenon in plating layers that contain magnesium metal, and is caused by incomplete oxidation of zinc metal due to preferential oxidation of magnesium metal concentrated on the surface. Blackening is the initial stage of metal corrosion, and when exposed to air, it tends to be easily completely oxidized to white rust. In particular, chromate treatment solutions are strong acidic aqueous solutions with a pH range of 1 to 1.5, and chromate products for building materials mainly have a problem that the thickness of the steel sheet is 1.0 mm or more, and cooling is not easy due to the latent heat after drying, making it difficult to sufficiently increase the drying temperature. To solve this problem, a technology has been proposed in which Co(III) salt is sprayed during the cooling process of the Zn-4.0%Al-0.1%Mg plating layer (ISIJ, 1990, p383-390), and more recently, a technology has been proposed in which an aqueous solution of Mg, Al, and Zn salts is treated on the surface of a Zn-Al-Mg alloy-plated steel sheet, followed by a zinc chloride aqueous solution (Korean Patent No. 10-1638307). However, this technology has problems in that the equipment required is complex and difficult to apply.

The present invention provides a chemical conversion treatment composition and a chemical conversion treatment method for preventing surface blackening defects that occur in Zn-Al-Mg alloy plated steel sheets and chromate-treated steel sheets.

According to one aspect of the present invention, a chemical conversion treatment composition for Zn-Al-Mg alloy-plated steel sheet is provided, which contains, based on the total weight of the chemical conversion treatment composition, 0.2 to 20 wt % of an amine phosphate salt derived from an alkyl phosphate acid and an alkylamine; 0.1 to 10 wt % of zinc phosphate; 0.1 to 10 wt % of a silicate compound; and the balance water.

According to another aspect of the present invention, a chemically treated steel sheet is provided, which includes a Zn-Al-Mg alloy plated steel sheet and a chemical conversion coating layer on at least one surface of the plated steel sheet, the chemical conversion coating layer being formed from the chemical conversion treatment composition.

The chemical conversion treatment composition according to the present invention can be adsorbed onto the surface of Zn-Al-Mg alloy plated steel sheets, and can prevent blackening caused by high temperature and high humidity environments or dew condensation during lamination of coils and steel sheets. .

1A shows a coating structure after chemical conversion treatment according to one embodiment of the present invention, and FIG. 1B shows a coating structure obtained by subjecting a chemically treated steel sheet to a chromate treatment. This figure shows a process of performing chemical conversion treatment and chromate treatment on a Zn-Al-Mg alloy plated steel sheet according to an embodiment of the present invention.

The following describes preferred embodiments of the present invention. However, the embodiments of the present invention can be modified in various different forms, and the scope of the present invention is not limited to the embodiments described below.

Normally, a chromate coating solution is a strong acid solution with a pH of 1.0 to 1.5. Therefore, during immersion, spraying or roll coating, the surface of the plating layer of the steel sheet is etched, and incomplete Cr-oxide or hydroxide precipitates to form a coating layer. In particular, due to equipment restrictions on the hot-dip plating line of steel manufacturers, the drying temperature for hardening the coating layer cannot be increased, and due to the problem of difficulty in cooling the steel sheet after drying, the coating layer is characterized by being dried at a temperature of 100°C or less. As a result, if the coil or stacked steel sheet is stored for a long period of time, the problem of blackening occurs on the surface. According to previous research, it is known that the blackening phenomenon occurs when the galvanized steel sheet is exposed to a high-temperature and high-humidity environment or an atmosphere with poor oxygen supply for a long period of time, or due to surface impurities or mechanical deformation. It is known that such a blackening phenomenon is likely to occur in a galvanized layer containing aluminum or magnesium, and is promoted by incomplete oxidation during the treatment with a phosphate compound or chromate on the surface of the plating layer.

As a method to solve the above-mentioned problems, as shown in Figure 1, impregnating the roughness formation site of the plating layer surface with an organic-inorganic corrosion-resistant phosphoric acid amine salt compound will prevent corrosion caused by highly acidic solutions. Corrosion phenomena can be prevented by preventing excessive surface etching and preventing acid from penetrating into rough areas or grain boundary areas of the plating layer. The present invention will be explained in detail below.

According to an embodiment of the present invention, a composition for chemical conversion treatment of a Zn-Al-Mg alloy plated steel sheet includes a phosphoric acid amine salt derived from an alkyl phosphate acid and an alkyl amine, zinc phosphate, a silicate compound, and the balance water. provided.

The amine phosphate may be a compound in which an alkyl phosphate acid and an alkylamine form an ionic bond. In the present invention, the amine phosphate may be included in an amount of 0.1 to 20% by weight based on the total weight of the chemical conversion treatment composition. If the content of the amine phosphate is less than 0.1% by weight, the effect of preventing blackening of the steel sheet is not fully exhibited, and if it exceeds 20% by weight, there is a problem that chromate coating is difficult in the subsequent chromate coating step.

The alkyl phosphate acid constituting the phosphoric acid amine salt may be a compound represented by the following chemical formula 1.

In the above formula 1, _R1 and _R2 are each independently a linear alkyl group having 3 to 15 carbon atoms or a branched alkyl group having 5 to 15 carbon atoms, and _R1 and _R2 may each independently be substituted with a hydroxyl group, an ether group, an ester group, or an epoxy group.

Preferred alkyl phosphate acids that can be used in the present invention are 2-ethylhexyl phosphate, isononanol phosphate, octyl ethoxylate phosphate, decyl ethoxylate phosphate, 2-ethylhexyl ethoxylate phosphate, decyl alcohol ethoxylate phosphate, and isotridecanol ethoxylate phosphate. ethoxylate phosphate, Tergitol 15-S-9 phosphate, Cetyl alcohol ethoxylate phosphate, Stearyl alcohol ethoxylate phosphate, Octyl alcohol ethoxylate phosphate, Oleyl alcohol ethoxylate phosphate, and Alkyl phenol ethoxylate phosphate The compound may be one or more selected from the group consisting of, but is not limited to, phosphate.

The alkylamine constituting the phosphoric acid amine salt may be at least one of the compounds represented by the following chemical formulas 2 to 8.

In the above chemical formulas 2 to 8, R ₃ , R ₄ and R ₅ are each independently hydrogen or methyl, R ₆ is each independently a linear or branched alkyl group having 3 to 5 carbon atoms substituted with a hydroxyl group, and n is an integer of 2 or 3.

Preferred alkylamines that can be used in the present invention include Bis(N-dimethylaminopropyl)amine, Bis(N-dimethylaminoethyl)methylamine, and Bis(N-dimethylaminoethyl)methylamine. (N-dimethylaminopropyl)methylamine (Bis(N-dimethylaminopropyl)methylamine), Bis(N-aminoethyl)methylamine, Bis(N-aminopropyl)methylamine N-aminopropyl)methylamine), Bis(dimethylaminoethyl)ether, Bis(dimethylaminopropyl)ether, Bis( aminoethyl)ether) , Bis(aminopropyl)ether, Bis(3-dimethylaminopropyl)isopropanolamine, 3-dimethylaminopropyldiisopropanolamine ropyldiisopropanolamine), 2 -(2-dimethylaminoethoxy)ethanol, 2-(2-dimethylaminoethoxyethyl)methylaminoethanol, 2-(2-dimethylaminoethoxyethyl)methylaminoethanol one or more selected from the group consisting of polynoethyl)ether (2-(2-dimethylphorinoethyl)ether) and 2-(2-dimethylaminoethyl)methylaminoethanol (2-(2-dimethylaminoethyl)methylaminoethanol); may be used, but is not limited to this.

The anion of the alkyl phosphate acid and the cation of the alkylamine form an amine phosphate salt through an ionic bond, and each can be contained in an amount of 0.1 to 10% by weight based on the total weight of the chemical conversion treatment composition.

In the chemical conversion coating composition according to one embodiment of the present invention, zinc phosphate forms phosphate crystals on the surface of the steel sheet when the composition is applied, imparting further corrosion resistance and blackening resistance. The zinc phosphate can be added in the range of 0.1 to 10 weight percent based on the total weight of the chemical conversion coating composition. If the zinc phosphate content is less than 0.1 weight percent, the corrosion resistance effect is minimal, and if it exceeds 10 weight percent, there is a problem that the chromate coating layer on the surface is easily cracked (brittle).

In the composition for chemical conversion treatment according to an embodiment of the present invention, the silicate compound precipitates on fine roughness areas on the surface of the steel sheet when the composition is applied, thereby imparting further corrosion resistance. The higher the content of the silicate compound, the better the corrosion resistance and the adhesion to the coating film, but even if it is added in a certain amount or more, there is a limit to the improvement in the corrosion resistance and the adhesion of the coating film. Therefore, the silicate compound is preferably added in an amount of 0.1 to 10% by weight based on the total weight of the chemical conversion treatment composition.

Silicate compounds that can be used in the present invention include lithium silicate, sodium silicate, potassium silicate, etc., and preferably lithium silicate compounds can be used.

The chemical conversion coating composition according to one embodiment of the present invention may further include a phosphate compound to adjust the acidity of the composition. The phosphate compound is added so that the pH of the composition is 3 to 5.

According to another aspect of the present invention, the Zn-Al-Mg alloy coated steel sheet subjected to chemical conversion treatment is prepared by the steps of alkaline degreasing, pickling, washing and drying of the cold-rolled steel sheet, and the steps of cooling after hot-dipping the zinc alloy. , a step of drying after chemical conversion treatment, and a step of drying after chromate treatment. At this time, the chemical conversion treatment composition and the chromate composition are treated by spraying followed by squeezing or roll coating, and drying is performed by hot air, infrared rays, or induction heating curing.

In the step of hot-dip plating the cold-rolled steel sheet with a zinc alloy, the zinc alloy may be in the form of Zn-xAl-yMg. In this case, it is preferable that x is 0.5 to 15 and y is 0.5 to 10.

In the stage of drying after the chemical conversion treatment, the chemical conversion treatment composition is preferably applied at 10 to 100 mg/ ^m2 , and can be dried at a temperature of 60 to 120° C. In addition, in the stage of drying after the chromate treatment, the composition can be preferably applied at 10 to 300 mg/ ^m2 based on the weight of the chromium element, and can be dried at a temperature of 80 to 120° C.

(Example)
Examples of the present invention will be described in detail below. The following examples are provided for understanding the invention and are not intended to limit it.
1. Examples (1) Production of composition for chemical conversion treatment Dissolve phosphoric acid amine salt consisting of isononanol phosphate and bis(N-aminoethyl)methylamine and zinc phosphate hydrate (DUCKSAN Chemical Company) in 1 L of pure water. A composition for chemical conversion treatment having a pH of 3.5 was prepared by adding a lithium silicate compound and phosphoric acid. The compositions of the above chemical conversion treatment compositions are shown in Table 1 below.

(2) Manufacture of chemical conversion treated steel sheet After applying the chemical conversion treatment composition manufactured above to a Zn-xAl-yMg plated steel sheet with a plating amount of 50 g/m ² and having the x and y values shown in Table 1 below. , and dried in a hot air oven at 80°C. A chromate (III) composition was applied to the above-mentioned chemical conversion treated steel plate by roll coating, and then dried in a hot air heating oven at 80°C. The chromate (III) composition has a solid content of 12% by weight and is a water-soluble Cr (III) composition (produced by Co., Ltd. ) NOROO coil coating) and the pH is 1.2.

2. Comparative Example Chromate (III) and chromate (VI) compositions were rolled on a Zn-xAl-yMg plated steel sheet with a plating amount of 50 g/m ² and x and y values shown in Table 2 below, as shown in Table 2 below. After applying the coating, it was dried in a hot air oven at 80° C. to produce a chromate-treated plated steel sheet.

3. Evaluation of Zn—Al—Mg alloy plated steel sheets The following items (1) to (5) were evaluated, and the evaluation results are shown in Table 3.
(1) [Cr] Coating Weight 30 ml of a 3% standard hydrochloric acid solution was added to the surface of the steel sheet to dissolve the plating layer, and then the [Cr] element was measured by ICP quantitative analysis.

(2) Resistance to blackening A test piece of 70 mm x 70 mm (width x length) was prepared from the coated steel plate, left at constant temperature and humidity (65°C, 95% relative humidity) for 120 hours, and compared with the original plate. The average color difference (ΔE) was measured.
<Evaluation criteria>
◎: When the average color difference (ΔE) is less than 5.0 ○: When the average color difference (ΔE) is 5.0 or more and less than 10.0 △: When the average color difference (ΔE) is 10.0 or more and less than 15.0 ×: When the average color difference (ΔE) is 15.0 or more

(3) Corrosion Resistance The corrosion resistance of the flat plate portion was evaluated by manufacturing a test piece of 70 mm x 150 mm (horizontal x vertical) from the steel plate, spraying salt water having a salt water concentration of 5% and a temperature of 35°C uniformly onto the test piece at a spray pressure of 1 kg/ ^cm2 , and then measuring the time until white rust appeared on 5% of the surface area of the steel plate. The corrosion resistance of the processed portion was evaluated in the same manner as above after the test piece was processed to 7 mm by Erichsen.
<Evaluation criteria>
◎: When the flat plate part is 168 hours or more. ○: When the flat plate part is 120 hours or more but less than 168 hours. △: When the flat plate part is 48 hours or more but less than 120 hours. ×: When the flat plate part is less than 48 hours.

(4) Alkaline Resistance Test pieces were prepared from steel sheets measuring 150 mm x 70 mm (horizontal x vertical). 20 g of strong alkaline degreasing agent DP FC-L4460A and 10 g of DP FC-L4460B (manufactured by Daehan Parkerizing Co., Ltd.) were dissolved in 1 L of pure water, and the test pieces were immersed at a temperature of 60°C for 2 minutes, and the average color difference (ΔE) was measured in comparison with the original sheet.
<Evaluation criteria>
◎: When the average color difference (ΔE) is less than 1.0 ○: When the average color difference (ΔE) is 1.0 or more and less than 1.5 △: When the average color difference (ΔE) is 1.5 or more and less than 2.0 ×: When the average color difference (ΔE) is 2.0 or more

(5) Corrosion Resistance to Pipe-Making Oil The steel sheet was immersed in 10% pipe-making oil for 24 hours and then the color difference after leaving it was measured and evaluated.
<Evaluation criteria>
◎: When the average color difference (ΔE) is less than 0.5 ○: When the average color difference (ΔE) is 0.5 or more and less than 1.0 △: When the average color difference (ΔE) is 1.0 or more and less than 1.5 ×: When the average color difference (ΔE) is 1.5 or more

As in Comparative Examples 1 to 4, when a chromate treatment was performed on a plated steel sheet without using a chemical conversion treatment composition, it was confirmed that the resistance to blackening was reduced.

Claims (9)

Based on the total weight of the chemical conversion treatment composition,
0.2 to 20% by weight of a phosphoric acid amine salt derived from an alkyl phosphate acid and an alkyl amine;
0.1 to 10% by weight of zinc phosphate;
A composition for chemical conversion treatment of a Zn-Al-Mg alloy-plated steel sheet, comprising: 0.1 to 10% by weight of a silicate compound (excluding _SiO2 and fluorosilicates); and the balance being water. The chemical conversion treatment composition for Zn-Al-Mg alloy plated steel sheet according to claim 1, wherein the alkyl phosphate acid is a compound represented by the following chemical formula 1:

(In the above formula 1, _R1 and _R2 are each independently a linear alkyl group having 3 to 15 carbon atoms or a branched alkyl group having 5 to 15 carbon atoms, and _R1 and _R2 may each independently be substituted with a hydroxyl group, an ether group, an ester group, or an epoxy group.) The composition for chemical conversion treatment of a Zn-Al-Mg alloy plated steel sheet according to claim 1, wherein the alkylamine is at least one of the compounds represented by the following chemical formulas 2 to 8.

(In the chemical formulas 2 to 8 above,
R ₃ , R ₄ and R ₅ are each independently hydrogen or methyl;
R ₆ is each independently a linear or branched alkyl group having 3 to 5 carbon atoms substituted with a hydroxy group,
n is an integer of 2 or 3. ) The alkyl phosphate acid is 2-ethylhexyl phosphate, isononanol phosphate, octyl ethoxylate phosphate, decyl ethoxylate phosphate, 2-ethylhexyl ethoxylate phosphate, decyl alcohol ethoxylate phosphate, isotridecanol ethoxylate phosphate, ethoxylate phosphate, Tergitol 15-S-9 phosphate, Cetyl alcohol ethoxylate phosphate, Stearyl alcohol ethoxylate phosphate, Octyl alcohol ethoxylate phosphate, Oleyl alcohol ethoxylate phosphate, and Alkyl phenol ethoxylate phosphate The chemical conversion treatment composition for Zn-Al-Mg alloy-plated steel sheet according to claim 1, which is at least one selected from the group consisting of phosphates. The alkylamines include Bis(N-dimethylaminopropyl)amine, Bis(N-dimethylaminoethyl)methylamine, and Bis(N-dimethylaminoethyl)methylamine. Bis(N-aminopropyl)methylamine, Bis(N-aminoethyl)methylamine, Bis(N-aminopropyl)methylamine ne ), Bis(dimethylaminoethyl)ether, Bis(dimethylaminopropyl)ether, Bis(aminoethyl)ether, Bis(aminopropyl) ) ether (Bis(aminopropyl)ether), Bis(3-dimethylaminopropyl)isopropanolamine (Bis(3-dimethylaminopropyl)isopropanolamine), 3-dimethylaminopropyldiisopropanolamine (3-dimethylaminopropyl) iisopropanolamine), 2-(2-dimethyl Ethanol) ethanol (2- (2 -Dimethylaminoethoxy) Ethanol), 2- (2 -dimethylaminominouetoxyethyl) Methylaminoe Tanol (2- (2 -Dimethylaminoethoxyethyl) MethylaminoEtha NOL), 2- (2 -dimethyl polyethyl) ether (2-(2-dimethylphorinoethyl)ether) and 2-(2-dimethylaminoethyl)methylaminoethanol (2-(2-dimethylaminoethyl)methylaminoethanol). A composition for chemical conversion treatment of a Zn-Al-Mg alloy plated steel sheet as described above. The composition for chemical conversion treatment of Zn-Al-Mg alloy-plated steel sheet according to claim 1, wherein the silicate compound is at least one selected from the group consisting of lithium silicate, sodium silicate, and potassium silicate. The chemical conversion treatment composition for Zn-Al-Mg alloy-plated steel sheet according to claim 1, further comprising the amine phosphate or a phosphate compound other than the zinc phosphate so that the pH of the composition is 3 to 5. On a Zn-Al-Mg alloy plated steel sheet,
The method includes the steps of applying the chemical conversion coating composition according to any one of claims 1 to 7 to at least one surface of the plated steel sheet and drying the composition to produce a chemical conversion coating layer ,
The method for producing a chemically treated steel sheet, wherein the coating layer is deposited at 10 to 100 mg/ ^m2 . The method for producing a chemically treated steel sheet according to claim 8, wherein a chromate coating layer is present on the chemical conversion coating layer.